Various methods for safely driving a vehicle such as an automobile have been devised. For example, there has been devised a method in which a camera for photographing the direction of travel of a vehicle is placed and a function of detecting a pedestrian or the like based on an image photographed by the camera is provided to a car navigation system. The car navigation system informs a driver of the presence of a pedestrian when the pedestrian is detected. The driver can drive a vehicle while keeping aware of the movement of a pedestrian.
As a method for detecting a pedestrian from an image photographed by a camera, we have a method using a neural network. A neural network is an information processing system which is created by using a cranial nervous system of a human being as a model, and is employed in not only detection of a pedestrian but also character recognition and the like.    Patent Document 1: Japanese Patent Application Publication No. 2008-21034
Patent Document 1 describes an image recognition apparatus for detecting a pedestrian from an image photographed by a camera mounted on a vehicle. The image recognition apparatus according to Patent Document 1 detects a candidate object which is a candidate for identification, from an input image with the use of a remarkability calculation method. By applying a neural network to a candidate object, whether or not the candidate object is a pedestrian is determined.
However, the quantity of calculation of a neural network (neuro calculation) is enormous. In a case where a pedestrian is detected from an image photographed by a camera with the use of neuro calculation, image recognition processing must be carried out in real time. Accordingly, there is a need to use a large-size hardware for neuro calculation. Also, in a case where neuro calculation is performed by software processing, a processor having a high clock frequency is indispensable, which causes a problem of increased power consumption.